Gas filled terminal bushing with protective check valve



April 14, 1964 G. J. EASLEY ETAL 3,129,276

GAS FILLED TERMINAL BUSHING WITH PROTECTIVE CHECK VALVE Filed May 29, 1959 5 Sheets-Sheet 1 q I I I-az I I I E SF6 I I I I I I 1 E I I' Fig.l WITNESSES: INVENTORS K Gilbert J. Eusley and qswvg Joanes H. Frukes.

B UM. M

ATTORNEY April 14, 1964 G. J. EASLEY ETAL 3,129,276

GAS FILLED TERMINAL BUSHING WITH PROTECTIVE CHECK VALVE Fig.4.

April 14, 1954 G. J. EASLEY ETAL 3,129,276

GAS FILLED. TERMINAL BUSHING WITH PROTECTIVE CHECK VALVE Filed May 29, 1959 3 Sheets-Sheet 3 United States Patent 3,129,276 GAS FILLED TERMINAL BUSHING WITH PROTECTIVE CHECK VALVE Gilbert J. Easley and James H. Frakes, Pittsburgh, Pa,

assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa, a corporation of Pennsylvania Filed May 29, 1959, Ser. No. 816,770 8 Claims. (Cl. 174-11.)

This invention relates to terminal bushings in general, and more particularly to entrance-type terminal bushings adapted for use with gas-filled apparatus.

It is a general object of the present invention to provide an improved terminal bushing adaptable for use with gas-filled apparatus, in which a protective device is included to prevent fnacturing of the weather-proof casing of the terminal bushing, upon an excessive rise of pressure within the interior of the enclosed gas-filled apparatus.

Another object is to provide an improved entrancetype terminal bushing adaptable for utilizing a portion of the dielectric gas of an associated gas-filled apparatus, in which valve structure is included to prevent complete loss of gas within the interior of the gas-filled apparatus, should a weather-proof casing, associated with the ter minal bushing, be cracked, or fractured during operation of the apparatus.

A more specific object of the present invention is to provide an improved entrance-type terminal bushing having a valve-controlled aperture provided in a barrier plate, associated with the grounded mounting flange of the terminal bushing, so that upon cracking, or fracturing of the weather-proof ceramic casing of the terminal bushing, said valve-controlled aperture will be closed, to prevent complete gas loss from the interior of the associated gas-filled electrical apparatus.

' In United States patent application filed September 14, 1956, Serial No. 609,915, now United States Patent 2,967,221, issued January 3, 1961 to Robert E. Friedrich, and assigned to the assignee of the instant application, there is disclosed and claimed a novel gas-tilled, circuitinterrupting apparatus utilizing a terminal bushing, which employs a part of the gas, associated with the interrupting apparatus, as a dielectric medium between the weatherproof porcelain casing of the terminal bushingand the dielectric body surrounding the terminal stud associated with the terminal bushing.

It is a further object of the present invention to improve upon the terminal-bushing construction, associated with such gas-filled apparatus, so that cracking, or fracturing of the porcelain weather-proof casing of the terminal bushing will not result in loss of gas pressure Within the gas-filled interrupting casing, and hence inability of the interrupterto open the connected circuit.

Further objects and advantages will readily become apparent upon reading the following specification, taken in conjunction with the drawings, in which:

FIGURE 1 illustrates a side elevational view, partly in vertical section, of a gas-filled circuit-interrupting structure employed in connection with a pair of entrance-type terminal bushings, constructed in accordance with the principles of the present invention;

FIG. 2 is an enlarged, vertical sectional view, taken through the left-hand arc-extinguishing unit of the gasfilled circuit-interrupting apparatus of FIG. 1, with the contact structure being illustrated in the closed-circuit position;

FIG. 3 is'an enlarged longitudinal vertical sectional view taken through the entrance-type terminal bushings of FIG. 1, illustrating the normally open position of the ICC valve in the barrier plate during normal operation of the circuit interrupter;

FIG. 4 is a considerably enlarged vertical sectional view taken through the normall, open valve construction utilized in connection with the barrier plate; and

FIG. 5 illustrates, fragmentarily, a modified type of terminal-bushing construction employing the principles of the present invention.

Referring to the drawings, and more particularly to FIG. 1 thereof, the reference numeral 1 generally designates gas-filled electrical apparatus, in this particular instance assuming the form of a double-break, sulfur-hexaflu-oride (SP gas-filled circuit interrupter. Associated with the gas-filled electrical apparatus 1 is a pair of entrance-type terminal bushings 2, utilized for carrying the current to a pair of serially related, arc-extinguishing units, generally designated by the reference numeral 3. The arc-extinguishing units 3 are identical in construction. They are electrically bridged by a conducting cross-bar 4, which is vertically actuated, in a reciprocal manner, by an insulating lift rod 5.

As well known by those skilled in the art, during the opening operation of the circuit interrupter, suitable mechanism operates to effect downward opening motion of the insulating lift rod 5. Since the lift rod 5 is fixedly secured to the conducting cross-bar 4, suitable contact structure associated with each arc-extinguishing unit is actuated, as described hereinafter, to effect thereby opening of the connected circuit by two serially related breaks.

, The lift rod 5 continues downwardly to a fully open-circuit isolating position, indicated by the dot-dash line 6,

thereby providing a pair of isolated break gaps in the controlled circuit.

With reference to FIG. 2, which illustrates more clearly the internal construction of the left-hand arc-extinguishing unit 3 of FIG. 1, it will be observed that there is provided a contact-foot adapter 8, threadedly secured to the lower threaded end 9 of the terminal stud 10, extending coaxially through the terminal bushing 2. Preferably the contact foot 8 includes a bifurcated portion 11 having apertures 12, through which extends a clamping bolt 13'.

Threadedly secured to the contact foot 8 is a relatively stationary, rod-shaped contact 14, which cooperates with a movable contact 15, the latter being associated with a puffer piston, generally designated by the reference numeral 16. The puffer piston 16 has a piston rod 17, which is biased downwardly in an opening direction by a battery of compression springs 18. The compression springs 18 bear at their lower ends upon a spring plate 19, which is threadedly secured to the lower end of the piston rod 17. A clamping nut 20 may additionally be employed. The upper ends of the accelerating springs 18 may seat upon the lower end 21 of an insulated operating cylinder, generally designated by the reference numeral 22, and constituting a casing for the arc-extinguishing unit 3.

During the opening operation, as mentioned hereinbefore, the lift rod 5 moves downwardly, carrying with it the conducting bridging bar 4. This will permit the opening accelerating compression springs 18 to expand, carrying the piston rod 17, movable contact 15 and piston puffer 16 downwardly. The downward motion of the puffer piston 16, within the operating cylinder 22, will compress gas, in this particular instance sulfur-hexafluoride gas, and will force the same upwardly through the orifice restriction 23 and into engagement with the are, not shown, established between the stationary and movable contacts 14, 15. In other words, the sulfur hexafiuoride gas within the region 24, below the puffer piston 16, is compressed by downward opening movement of the putter piston 16, and is forced upwardly adjacent the arc andout apertures 25, associated with the upper contact foot 8 of the arc-extinguishing unit 3.

The terminal-bushing construction 2 is more clearly illustrated in FIG. 3 of the drawings. With reference to -FI G. 3,.it will be noted that the terminal bushing 2 includes a longitudinally extending terminal stud 10, of rod-shaped-configuration, which extends. coaxially longitudinally through the terminal bushing 2, and is surrounded, or at leastpartly enveloped by a generally cylindrically-shaped dielectric body, by the reference numeral 27.

' The dielectric body 27 may assume a number of different forms. For example, the dielectric body 27 may beformed, by wrappingv a number of layers of suitable impregnated paper about the centrally disposed terminal generally designated stud 10. Also the dielectric body 27 could be formedof molded insulating material, which is molded about the terminalstud' 10. However, the space 28, between the dielectric. body 27 and the inner wall 29 of a ceramic weather-proof casing 30, is filled with the same gas, which is present within the region 31 within the grounded tank 32 of the circuit-interrupting structure 1.'

A barrier plate 33, in this particular instance assuming the form of a radially inwardly extending flange portion of'the grounded mounting support34, separates the gas space, or region 28 from the region 31 Within the tank structure 32; One or more apertures 35, more clearly illustrated in FIG. 4, are-provided in the barrier plate 41in a flange support 42 which constitutes the upper end of,a cylindricalsupport 43, which is preferably welded to the cover 44 of the tank structure 32. As a result, the terminal bushing 2 is fixedly secured into position, and the arc-extinguishing units 3 likewise are into position.

There may occur, during times of high-current'interruption, excessive momentary pressures within the internal region 31within tankstructure 32. Thus, during heavyarcing conditions, the pressure within region 31, interiorly of the tank 32, degree. To prevent this excessive pressure acting through the apertures 35 of barrier plate 33, upon the porcelain casing 30, it is proposed to control the gas passage, through apertures 35, by the use of a normally-open valve, generally designated by the reference numeral 45, and assuming a construction more clearly shown in FIG. 4 of the drawings. As illustrated in FIG. 4, a valve plate 46 has a valve stem 47, encircling which is a compression spring 48, which tends to bias the-valve plate 46 downwardly to an open position away from the valve seat 49. Thus, during normal operation of the interrupting structure 1, the valve disc 46 is in its lower open position, being biased-open by the biasing means 50, comprising the biasing spring 48. During the existence of heavy pressure conditions within the region 31 within tank structure 32, such excessive pressure will cause the valve disc 46 to become seated upon valve seat 49 to prevent, thereby, this excessive pressure from being transmitted through the valve structure 45 and into the gas space 28. As a result, the somewhat fragile-ceramic casing 30, which may be made of porcelain, is not subjected to the aforesaid heavy pressure occurring within space 31, caused by heavycurrent interrupting operations. This advantageously results in protecting the porcelain casing 30 from the imposition of such an. excessive pressure thereon, and

a possible consequent cracking, or explosion of the percelain casing 39 occurring.

In an outdoor power circuit interrupter using gas, such fixedly secured:

may momentarily rise to a considerable,

sulating medium, it seems logical to take advantageuof.

the good insulating properties of this gas by using it as the insulation for the entrance terminal bushings, instead of the more expensive bushings made of solid insulation, such as the paper-wound condenser type. However, for certain applications, the gas-filled bushing has a disadvantage that must be recognized.

In a properly co-ordinated breaker, the external insulation (porcelain) on the entrance bushings should flash over at a lower value of voltage than the internal insulation of the breaker. The reason for this is that even though a voltage surge may flash over the external insulation, and probably damage the porcelain casingin the process, the breaker is still able to-interrupt, the fault successfully.

Unfortunately, when a gas-filled terminal bushing is used, a porcelain casing broken as a result of an external.

flashover will release the gas from the interior ofthe breaker pole unit, so that the breaker pole unit will not be able to interrupt the fault successfully. Using an independent supply of gas for the bushinginsulation is not possible, unless a solid insulating barrier is used, thatv amounts to an entrance bushing withvsolid insulation.

Assuming then, for certain applications, that a con-.

increased maintenance by the customer in the field, as well.

as extra handling during manufacture.

The problem may be solved by having a passageway between the gas within the bushing space 28 and the gas,

within the interior 31 of the pole unit,- that is open for normalconditions, and closed when the porcelain casing 30 breaks. As illustrated in FIG. 3, a one-way acting valve45 may be utilized in the passageway. The valve disc-46-of the valve structure 45 may be biased downwardly, by the spring 48, so that it is open under normal conditions, and the dielectric gas may flow freely between the'two chambers 28 and' 31. If, however, the bushing porcelain casing 30 cracks,- or breaks, the sudden loss of pressure within the gas space 28- will cause the valve disc 46 to snap shut, thusholding the dielectric gas within the interior 31 of the pole unit for successful breaker operation. The terminal bushing 2 will then hold voltage for an indefinite period, even with a broken porcelain casing 30, until repairs can be made. Since filling the pole unit l-with the dielectric gas, such as sulfur hexafluoride gas, is a relatively slow operation, the valve structure 45'will remain open so as not to interfere with this process, either during manufacture or during field maintenance.

For certain applications, involving relatively low voltage, andfor certain other specific applications, the modified terminal bushing construction 52, fragmentarily illustrated in FIG. Smay be employed. The construction here is identical to that of FIG. 3, except'the dielectric body 27 is omitted, and only the conductor rod 10 is employed. Also, the barrier plate 33A is formed of insulating material, since full voltage is impressed between the terminal stud 10 and the grounded mounting flange support 34A, The valvev structure 45 may be identical to the valve structure 45 illustrated in detail in FIG. 4 ofv the drawing.

With the modified terminal-bushing construction in FIG. 5, should the porcelain casing 30 break or fracture, atmospheric air wouldleak into the bushing space 28, lowering the pressure therein. This drop of pressure within gas space 28, of terminal bushing 52 would, as before,

cause closure of valve structure '45 to prevent loss of gas within the'space 31 internally of tank structure 32.

Although FIG. 1 illustrates the terminal bushings 2 of the present invention employed with a gas-filled circuitinterrupting apparatus 1, it is to be clearly understood that the terminal bushings 2 may be employed with other gas-filled electric apparatus, such as transformers, etc., where it is desirable to utilize a portion of the dielectric gas within the gas-filled apparatus to provide additional dielectric within the terminal bushing itself. Merely for purposes of illustration has the invention been described as applied to a gas-filled circuit interrupting apparatus 1. Also, although sulfur-hexafluoride (SP gas has been described in connection with FIG. 1, it is to be clearly understood that the present invention is applicable with any suitable dielectric gas, not necessarily sulfur hexafluoride gas. For example, carbon dioxide, helium, argon, nitrogen, or selenium hexafluoride may be employed as the dielectric gas. Merely for purposes of illustration has sulfur hexafluoride been described as the insulating and dielectric gas.

The broad concept of utilizing sulfur-hexafluoride (SP gas in a terminal bushing is described and claimed in United States patent application filed December 2, 1959, Serial No. 856,776, new Patent No. 3,059,044, issued October 16, 1962, to Robert E. Friedrich and James H. Frakes, and assigned to the assignee of the instant application.

The particular are extinguishing units 3 of FIG. 1 are set forth and claimed in United States patent application filed September 27, 1957, Serial No. 686,775, now United States divisional Patent 2,965,736, issued December 20, 1960 to Thomas E. Browne, Jr. and Albert P. Strom, and assigned to the assignee of the instant application.

Although there have been illustrated particular terminal-bushing constructions employed in conjunction with interrupting gas-filled apparatus, it is to be clearly understood that the same were merely for the purpose of illustration, and that changes and modifications may be readily made therein by those skilled in the art, without departing from the spirit and scope of the invention.

We claim as our invention:

1. In combination, an entrance-type terminal bushing at least partially filled with gas and utilized in connection with gas-filled electrical apparatus, such as circuit interrupters, transformers, or the like, including a terminal stud extending longitudinally through the said entrancetype terminal bushing, a dielectric body surrounding at least a portion of the longitudinal length of said terminal stud for dielectric purposes, a weather-proof casing for the terminal bushing disposed externally of the said electrical apparatus and susceptible of being fractured, a barrier plate constituting a part of the terminal bushing and separating the gas space between the dielectric body and the weather-proof casing from the interior gas space within the electrical apparatus, an aperture in said barrier plate, and only normally-open unidirectional check valve means associated with said barrier plate for controlling the gas passage through said aperture and adapted to close upon loss of pressure within said first-mentioned gas space.

2. An entrance-type terminal bushing at least partially filled with gas and including a grounded mounting flange, a terminal stud for the terminal bushing having a dielectric body disposed thereabout, a weather-proof casing of a ceramic material, a gas space between said weatherproof casing and said dielectric body, a barrier plate constituting a part of the terminal bushing and associated with said grounded mounting flange, said barrier plate having an opening therethrough, and only normally open check valve means for controlling said opening for stopping flow of gas through said opening upon loss of pressure within said gas space.

3. A terminal bushing at least partially filled with gas and including a frangible casing, a conductor rod extending through the terminal bushing, a barrier plate constituting a part of the terminal bushing and disposed substantially midway between the ends of the terminal bushing, said barrier plate separating one end of the terminal bushing from the other end of the terminal bushing, an aperture provided in the barrier plate, and only normallyopen one way acting valve means controlling the passage of gas through the aperture in the barrier plate.

4. A terminal bushing at least partially filled with gas and including a frangible casing, a conductor rod extending through the terminal bushing, an insulating barrier plate disposed substantially midway between the ends of the terminal bushing and separating one end of the terminal bushing from the other end of the terminal bushing, an aperture provided in the barrier plate, and only one-way acting normally-open check valve means controlling the passage of gas through the aperture in the barrier plate to stop the flow of gas therethrough in the direction of said casing upon a drop of gas pressure within the casing.

5. The combination in a terminal bushing at least partially filled with gas and employed in conjunction with gas-filled electrical apparatus of a ceramic casing, a conductor rod extending through the terminal bushing, a barrier plate, a grounded flange support, said barrier plate extending between the grounded flange support and the conductor rod, an opening provided in the barrier plate, and only unidirectionally-acting normally-open checkvalve means controlling the flow of gas through said opening, whereby loss of pressure on the ceramic-casing side of said barrier plate will effect closure of said check-valve means to prevent total loss of the gas.

6. An entrance-type terminal bushing at least partially filled with gas and utilized in connection with gas-filled electrical apparatus including an outer part which extends externally of the gas-filled electrical apparatus and an inner part protruding within the gas-filled electrical apparatus, a conductor stud extending longitudinally through the terminal bushing, a ceramic weather-proof casing disposed about the outer part of the terminal bushing, a barrier plate separating the outer part of the terminal bushing from the inner part of the terminal bushing, an aperture through the barrier plate, and only a normally open check valve for controlling the gas flow through said aperture.

7. A terminal bushing at least partially filled with gas and including a longitudinally extending conductor stud and a surrounding solid dielectric body enclosing a substantial axial length of the conductor stud, a mounting ground-flange structure for supporting the terminal bushing in an operative position on a tank wall, or the like, the ground flange structure supporting the exterior surface of the dielectric body adjacent the mid-portion thereof, a frangible weather-proof shell extending between the ground-flange structure and the normally externally disposed end of the terminal bushing when the same is mounted in an operative position, a gas space between the frangible shell and the exterior surface of the dielectric body, and only a check valve-controlled opening in the ground-flange structure, said opening being normallyopen and adaptable to be closed upon a drop of pressure within said gas space.

8. The combination in a gas-filled terminal bushing of an axially extending conductor stud, a frangible weatherproof shell protecting the externally disposed end of the conductor stud, supporting ground-flange structure disposed adjacent the mid-portion of the terminal bushing and adaptable to support the terminal bushing in an operative position within a tank wall, or the like, an insulating supporting barrier plate extending inwardly from the ground-flange structure and closing the inner end of the gas space between the outer shell and the conductor stud, and only a check valve-controlled opening provided in said barrier plate, said opening being normally-open and 8. adaptable, tohe closedupon a drop of pressure within the 2, 447,8,83- Whitman Aug. 24, 1948 gas space. 2,459,612 Baker I an. 18, 1949 2,520,111 Bennett Aug. 29, 1950 References Cited 'in.the file of this patent. 2,647,939 Paluev Aug. 4, 1953 UNITED STATES PATENTS; FOREIGNv PATENTS 2,116,419 Wetherill May 3, 19 8' 601,905 Germany Aug. 27, 1934 2,180,425 Meyer NOV. 21, 1939' 650,086 Great Britain Feb. 14, 1951 

2. AN ENTRANCE-TYPE TERMINAL BUSHING AT LEAST PARTIALLY FILLED WITH GAS AND INCLUDING A GROUNDED MOUNTING FLANGE, A TERMINAL STUD FOR THE TERMINAL BUSHING HAVING A DIELECTRIC BODY DISPOSED THEREABOUT, A WEATHER-PROOF CASING OF A CERAMIC MATERIAL, A GAS SPACE BETWEEN SAID WEATHERPROOF CASING AND SAID DIELECTRIC BODY, A BARRIER PLATE CONSTITUTING A PART OF THE TERMINAL BUSHING AND ASSOCIATED WITH SAID GROUNDED MOUNTING FLANGE, SAID BARRIER PLATE 